Chemical reactions are commonly carried out in reactors in which molecules are forced to interact with heated catalysts to produce a desired chemical product or products. Precise heating of the catalyst is used to ensure that desired products are produced at desired yields, concentrations, and purities. When the temperature is too high, unwanted chemical reactions may occur. When the temperature is too low, the catalyst is generally insufficiently active to produce the desired product or products. The input reactant or reactants generally react to produce the desired product or products only when they are in intimate contact with the catalyst. Chemical reactors therefore feature tightly constrained spaces containing precisely-heated catalyst particles.
Known systems permit hydrogen storage and release using an organic hydrocarbon hydrogen carrier molecule, which releases hydrogen by the action of a catalyst and heat. To provide a large surface area, a core having parallel microchannels is employed, through which the organic hydrocarbon hydrogen carrier molecule flows, contacting catalytic surfaces of the microchannels.
Current designs are very inefficient because heat has to move from exterior heaters to channels deep within the core's interior. Heat moves from hot outer surfaces to the cooler inner surfaces via conduction along the thin channel walls. This requires that the heat on the outside channels be much higher than the desired heat on the inner channels. The heat differential is typically quite extreme, up to 100° C. or more. This range of temperatures may result in inefficient operation, and/or unintended or undesirable chemical decomposition.
A typical multi-channel reactor has a ceramic core with channels having square cross-sections measuring approximately 1 mm on a side, running parallel down the length of the core. The length of the core is chosen so that there is a high probability of reaction by the end of the microchannel. The number of channels is usually a function of flow rate and reaction rate and the expected portion of unreacted molecules at the exit of the channels. The number of channels can be from hundreds to thousands, in some designs.
For reactions that are endothermic, such as those carried out within an automobile catalytic converter, the engine heat is used to heat the channel surfaces before the final reaction occurs. However, not all catalytic converters are attached to a heat generating engine or heat source, and thus require external heat in order to maintain the catalyst within an appropriate range of temperatures.
Currently available reactors for this type of system have external heating elements attached to the outside housing of the cores. This type of design is very inefficient, since the heat has to move from the exterior heaters to the channels deep within the core interior. The core is typically designed for high surface area per volume or weight, and therefore the wall conduction of heat to the center of the core is poor. This makes the outside channels reach a higher temperature than the inner channels. The heat differential may be quite extreme, on the order of a 100 degrees Celsius or more. This extreme difference makes the channels on the outside too hot and creates the potential for unwanted side reactions of the organic hydrocarbon hydrogen carrier molecule.
Application of the catalyst to the side walls of the channels is also suboptimal in currently available chemical reactors. Currently, the practice is to dip the core into a slurry bath where the slurry consists of a suspension with a small percentage of catalyst with alumina and water with a viscosity like wheat paste. The alumina is used as the mechanism to bind the catalyst to the core channels. The problem with this technique is that the mixture is not homogeneous. It's hard to tell where the catalyst is within the mixture. Because the mixture is not homogeneous, some channels have no catalyst while others have too much.
Inductively heated catalytic systems are disclosed in, e.g.: 20170334822; 20170321233; 20170283258; 20170260328; 20170252872; 20170233546; 20170226907; 20170218823; 20170218816; 20170210892; 20170190629; 20170183477; 20170170477; 20170158840; 20170152532; 20170145886; 20170130252; 20170128927; 20170121737; 20170101528; 20170101312; 20170089304; 20170080697; 20170079325; 20170022868; 20170022062; 20170014765; 20170014764; 20170014763; 20170009061; 20170009060; 20170000145; 20160298147; 20160298141; 20160293990; 20160289710; 20160289709; 20160289706; 20160289705; 20160289704; 20160289577; 20160281482; 20160265159; 20160257783; 20160257067; 20160251535; 20160237591; 20160225490; 20160167010; 20160165926; 20160160240; 20160090614; 20160075953; 20160038906; 20160038905; 20160033492; 20160032341; 20160024374; 20160009554; 20150368762; 20150354426; 20150353974; 20150344914; 20150344143; 20150342224; 20150329879; 20150299494; 20150275108; 20150267036; 20150265997; 20150234304; 20150217260; 20150211730; 20150203701; 20150184090; 20150183641; 20150152344; 20150122802; 20150122529; 20150122243; 20150104843; 20150075839; 20150044122; 20150021094; 20150004669; 20140374237; 20140348982; 20140334999; 20140329961; 20140329280; 20140329091; 20140197854; 20140197154; 20140183185; 20140182563; 20140182366; 20140182272; 20140154749; 20140148568; 20140147907; 20140033777; 20140030768; 20140030763; 20130315028; 20130303810; 20130295624; 20130288307; 20130273612; 20130266556; 20130261340; 20130225714; 20130216520; 20130196386; 20130183735; 20130175068; 20130164818; 20130150533; 20130122764; 20130102029; 20130101326; 20130056209; 20130026752; 20130011895; 20120316376; 20120315060; 20120309100; 20120309060; 20120291343; 20120289734; 20120283449; 20120277329; 20120268219; 20120267448; 20120267359; 20120237984; 20120231197; 20120215023; 20120203021; 20120202994; 20120142068; 20120142065; 20120094358; 20120094355; 20120077247; 20120065307; 20120039781; 20120017422; 20120003704; 20110303532; 20110301363; 20110300029; 20110297623; 20110272082; 20110271588; 20110232169; 20110209897; 20110179907; 20110155559; 20110147639; 20110147041; 20110111456; 20110094772; 20110081336; 20110081335; 20110067576; 20110056124; 20110052460; 20110042201; 20110042084; 20110039317; 20110027837; 20110008246; 20100316882; 20100304440; 20100304439; 20100258309; 20100258291; 20100258290; 20100258265; 20100249404; 20100224368; 20100209056; 20100206570; 20100179315; 20100155070; 20100147522; 20100147521; 20100124583; 20100112242; 20100108567; 20100108379; 20100108310; 20100101823; 20100101794; 20100101784; 20100101783; 20100096137; 20100089586; 20100089584; 20100087687; 20100072429; 20100071904; 20100071903; 20100069656; 20100055349; 20100032308; 20100021748; 20090311445; 20090286295; 20090272578; 20090272536; 20090272535; 20090272533; 20090272526; 20090260824; 20090260823; 20090257945; 20090236329; 20090233349; 20090208684; 20090200854; 20090200290; 20090200031; 20090200025; 20090200023; 20090200022; 20090194524; 20090194333; 20090194329; 20090194287; 20090194286; 20090194282; 20090194269; 20090189617; 20090184281; 20090074905; 20090074630; 20090025425; 20090023821; 20090014121; 20090011180; 20080319375; 20080311045; 20080294089; 20080274280; 20080264330; 20080243049; 20080223851; 20080197534; 20080187907; 20080182911; 20080182027; 20080156228; 20080149363; 20080142367; 20080124994; 20080035682; 20070210075; 20070204512; 20070110985; 20070068933; 20060289481; 20060115595; 20060068080; 20060051281; 20050287297; 20050255370; 20050212297; 20050208218; 20050121437; 20050107251; 20040249037; 20040229295; 20040185384; 20040180203; 20040170820; 20040157002; 20040155096; 20040150311; 20040149737; 20040149297; 20040139888; 20040129555; 20040127012; 20040076810; 20040050839; 20030220039; 20030212179; 20030207112; 20030175196; 20030121909; 20030075540; 20030071033; 20020102353; 20010024716; U.S. Pat. Nos. 9,803,222; 9,758,638; 9,745,609; 9,745,604; 9,700,868; 9,695,280; 9,676,491; 9,657,622; 9,618,947; 9,607,732; 9,605,288; 9,605,287; 9,587,258; 9,528,322; 9,517,444; 9,493,796; 9,475,698; 9,446,371; 9,409,140; 9,404,005; 9,400,439; 9,352,294; 9,347,661; 9,334,843; 9,309,545; 9,290,780; 9,285,403; 9,283,537; 9,278,896; 9,212,591; 9,208,923; 9,187,769; 9,186,646; 9,175,137; 9,163,114; 9,138,715; 9,132,407; 9,129,728; 9,109,241; 9,101,880; 9,089,628; 9,078,461; 9,074,566; 9,062,328; 9,058,918; 9,051,829; 9,044,900; 9,023,628; 9,023,183; 9,022,118; 9,010,428; 8,999,030; 8,980,602; 8,946,489; 8,900,839; 8,881,806; 8,877,472; 8,876,923; 8,871,964; 8,852,905; 8,852,896; 8,851,170; 8,849,142; 8,846,356; 8,841,101; 8,835,142; 8,771,480; 8,764,978; 8,764,948; 8,763,231; 8,752,904; 8,747,624; 8,734,654; 8,734,643; 8,728,779; 8,716,537; 8,709,771; 8,709,768; 8,708,691; 8,680,399; 8,647,401; 8,637,284; 8,636,323; 8,609,384; 8,603,787; 8,597,921; 8,576,017; 8,576,016; 8,569,526; 8,568,507; 8,562,078; 8,536,497; 8,529,738; 8,518,683; 8,497,366; 8,492,128; 8,475,760; 8,455,580; 8,454,803; 8,448,707; 8,434,555; 8,414,664; 8,382,970; 8,372,327; 8,362,407; 8,357,883; 8,353,347; 8,329,936; 8,327,932; 8,292,987; 8,281,861; 8,276,661; 8,276,636; 8,272,455; 8,267,185; 8,267,170; 8,261,832; 8,256,512; 8,240,774; 8,236,535; 8,220,539; 8,212,087; 8,197,889; 8,196,658; 8,192,809; 8,177,305; 8,172,335; 8,168,038; 8,162,405; 8,162,059; 8,158,818; 8,153,942; 8,151,907; 8,146,669; 8,146,661; 8,142,620; 8,113,272; 8,083,906; 8,080,735; 8,057,666; 8,017,892; 8,011,451; 7,976,692; 7,955,508; 7,932,065; 7,931,784; 7,866,388; 7,866,386; 7,863,522; 7,827,822; 7,816,415; 7,816,006; 7,794,797; 7,776,383; 7,745,355; 7,713,350; 7,655,703; 7,569,624; 7,559,494; 7,517,829; 7,473,873; 7,413,793; 7,390,360; 7,387,673; 7,365,289; 7,361,207; 7,341,285; 7,323,666; 7,233,101; 7,205,513; 7,185,659; 7,168,534; 7,070,743; 7,033,650; 6,926,949; 6,858,521; 6,858,302; 6,849,837; 6,849,109; 6,830,822; 6,803,550; 6,726,962; 6,710,314; 6,689,252; 6,639,198; 6,639,197; 6,630,113; 6,624,337; 6,603,054; 6,509,555; 6,383,706; 6,315,972; 6,261,679; 6,215,678; 6,086,792; 6,066,825; 6,018,471; 6,001,204; 5,958,273; 5,878,752; 5,847,353; 5,846,495; 5,820,835; 5,781,289; 5,737,839; 5,651,906; 5,443,727; 5,423,372; 5,350,003; 5,325,601; 5,321,896; 5,240,682; 5,200,145; 5,152,048; 5,110,996; 5,075,090; 4,952,539; 4,921,531; 4,729,891; 4,716,064; 4,237,111; 4,105,455; and 3,972,372, each of which is expressly incorporated herein by reference in its entirety. Catalysts may be produced according to, e.g., U.S. 20140187416, and U.S. Pat. No. 9,421,523.
Organic chemical hydrides employ hydrogenation-dehydrogenation of cyclic hydrocarbons or heteroaromatic compounds as a means to store and transport hydrogen. Aromatic compounds, such as benzene, toluene, and naphthalene can be hydrogenated by using appropriate metal catalysts under relatively mild conditions, e.g. about 100° C. and 2 MPa. However, the dehydrogenation of cyclic hydrocarbons is endothermic and the reaction is favored only at high temperatures as well as having problems with coking on catalyst surfaces requiring catalyst regeneration every 1-2 hours. Catalytic dehydrogenation under “liquid-film state” conditions has been reported (Meng et al., Int. J. Hydrogen Energy 22:361-367, 1997; Hodoshima et al., Int. J. Hydrogen Energy 28; 197-204, 2003; Hodoshima et al., Appl. Catal. A: Gen. 292:90-96, 2005; and Hodoshima et al., Appl. Catal. A: Gen. 283:235-242, 2005), where the reactant is supplied as a liquid so that the surface of the catalyst is wetted with a thin film. Equilibrium limits were surpassed because of evaporation of the dehydrogenated reactants. Another method uses “wet-dry multiphase conditions” to take advantage of multiple phases to get over thermodynamic equilibrium limitations (Kariya et al., Appl. Catal. A: Gen. 247:247-259, 2003; and Kariya et al., Appl. Catal. A: Gen 233:91-102, 2002). However, both processes still require relatively high temperatures for vaporization of the volatile components of the process. An important need is also an effective separation of hydrogen from the mixtures to get a pure hydrogen product and to reuse the hydrogen carrier materials.
Hydrogen may be produced by reacting a compound capable of producing hydrogen and having the formula R—XH, with a catalytic substrate to produce hydrogen gas. See, US 20070003476, 20080045408, 20080045412, 20090093886, U.S. Pat. Nos. 7,186,396, 8,459,032, and 8,535,381.
The R group includes, for example, a moiety selected from an alkyl, heteroalkyl, alkenyl, substituted alkenyl, substituted alkyl, alkynyl, aryl, heteroaryl, alkoxy, cycloalkyl, heterocyclic, alkylaryl, arylalkyl, arylalkenyl, arylalkynyl, arylene, oxyarylene group, and combinations thereof. The compound may be a liquid at standard temperature and pressure. X can include sulfur, oxygen, or selenium, or other heteroatoms, such as nitrogen, phosphorus, and boron. Sulfur is a typically heteroatom, and the compound may be an organothiol. As used herein, “substituted” refers to organic or heterorganic groups further bearing one or more substituents selected from hydroxy, alkoxy, mercapto, cycloalkyl, substituted cycloalkyl, heterocyclic, substituted heterocyclic, aryl, substituted aryl, heteroaryl, substituted heteroaryl, aryloxy, substituted aryloxy, halogen, cyano, nitro, amino, amido, —C(O)H, acyl, oxyacyl, carboxyl, sulfonyl, sulfonamide, sulfuryl, and the like. Known compounds suitable for storage and production of hydrogen by dehydrogenation of hydrocarbon moiety include, for example, butanethiol, pentanethiol, hexanethiol, cyclohexanethiol, and 1,4-cyclohexandithiol.
Heteroatom aromatic rings for H2 storage were proposed because the addition of electron-donating groups favors H2 release both thermodynamically and kinetically at moderate temperatures. In the case of indoline, dehydrogenation is possible at modest temperature (110° C.) (Moores et al., New J. Chem. 30:1675-1678, 2006). Benzimidazolines, including N,N′-dimethyldihydrobenzimidazole, 1,3-dimethyl-2-phenylbenzimidazoline, and 1,3-dimethylbenzimidazoline, were studied with different palladium catalysts, releasing H.sub.2 even at 80.degree. C. (Schwarz et al., Chem. Commun. 5919-5921, 2005).
However, hydrogen density is an important factor in hydrogen storage. Therefore, a high hydrogen/weight ratio is desired while maintaining favorable thermochemical and kinetic parameters. Smaller molecules, such as 4-aminopiperidine and piperidine-4-carboxamide are proposed compounds for reversible hydrogen storage (Cui et al., New J. Chem. 32:1027-1037, 2008). Dehydrogenation and hydrogenation of 4-aminopiperidine and piperidine-4-carboxamide occur at low temperatures without by-products, such as C—N cleavage and hydrogenolysis products. Dehydrogenation may be favored in five-membered rings over six member rings and by the incorporation of N heteroatoms into the rings, either as ring atoms or as ring substituents, particularly in 1, 3 positions (Clot et al. Chem. Commun. 2231-2233, 2007). Heteroaromatic ligands have been used for reversible hydrogenation/dehydrogenation, specifically N-ethyl carbazole hydrogenated with 72 atm and a Pd catalyst at 160° C. and dehydrogenated with Ru at 50-197° C. See, U.S. Pat. Nos. 7,351,395, and 7,186,396.
One form of hydrogen fuel for release, storage and recycling of hydrogen fuels uses a sulfur-containing heteroatom that is cyclized on dehygrogenation and when re-hydrogenated the ring is broken to form a linear, thiol-containing alkane moiety.
Spent forms of recyclable liquid fuels that release hydrogen gas, include aromatic compounds such as benzene and naphthlene (aromatic substrates) that undergo reversible hydrogenation to form cyclohexane and decalin, respectively. U.S. Pat. No. 6,074,447, for example, describes dehydrogenating methylcyclohexane, decalin, dicyclohexyl, and cyclohexane to toluene, naphthalene, biphenyl and benzene, respectively in the presence of an iridium catalyst at temperatures of 190° C. or higher. Yet even at such temperatures, hydrogen release reactions require several minutes for full release and often exist as solids at room temperatures.
Catalytic metal substrates suitable for reacting with the compound to produce hydrogen can include, for example, gold, silver, platinum, copper, and mercury. Metal substrates can include pure metal substrates as well mixtures of metals, such as metal alloys and a polymer coated with metals. The metal may be nanoporous, or provided as nanoparticles.
The hydrogen so produced may be used in mobile applications, such as vehicles and electronic devices, and may be combusted, consumed in a fuel cell, or used in a chemical reaction.
The compound capable of producing hydrogen is preferably suitable for re-use, in that spent compound is capable of being regenerated. A spent compound can include, for example, a dimeric compound, such as a compound having a formula R—X—X—R. The energy source used to drive the endothermic hydrogen release reaction can include, for example, a heat source or a UV light source.
In normal catalytic hydrogenation, the catalyst surface breaks the bond between hydrogen molecule homolytically (H—H 436 kJ/mole) and the catalyst forms a new bond with hydrogen. Because the metal-hydrogen bonds lack stability, the hydrogen atoms can leave the surface as hydrogen gas. A hydrocarbon moiety (e.g., R as defined above) of the hydrogen producing compound is typically the source of hydrogen.
The dehydrogenation reaction of the organic compound is endothermic, and requires an external heat source for continuous operation. It is known to provide a thermocouple integrated into walls of a microchannel reactor. See, e.g., U.S. 20090185964, and U.S. Pat. No. 8,092,558.
According to one process, hydrogen is released from an alkane thiol and capturing a dehydrogenated product. Specifically, the disclosed process for releasing hydrogen gas from a C5-7 alkane thiol comprises: providing an alkane thiol in a gaseous phase; exposing the alkane thiol to a catalyst having particle sizes of about 2 nm to 500 nm, at a temperature of from about 150° C. to about 300° C. to form a five-membered cyclic thioether, substituted with from 1-2 methyl or ethyl groups and at least one mole of diatomic hydrogen gas; and exposing the cyclic thioether product to another catalyst at a temperature of from about 130° C. to about 400° C. to form a thiophene and two more moles of diatomic hydrogen gas. See, U.S. 20110020214, and U.S. Pat. No. 9,623,393. Preferably, the initial catalyst has an average particle size of from about 500 nm to about 2 nm, comprising gold without nickel or chrome. The catalyst may be a particle selected from the group consisting of Au/TiO2, Pt/SiO2, Ag/SO2, Au/Al2O3, Pt/Al2O3, Pd/Al2O3, Rh/Al2O3, and combinations of metals Au, Pt, Ag, Au, Pt, Pd and Rh with ceramic particles selected from the group consisting of TiO2, SO2, SiO2, Al2O3 and combinations thereof. The process may further capture the cyclic thioether as a liquid or gaseous phase. The alkane thiol may be a pentane thiol or a hexane thiol or a heptane thiol, each having the thiol moiety at the N1 position or a mixture thereof. The second catalyst surface may be is a platinum or gold or platinum/gold combination catalyst surface. See, U.S. 20110020214, U.S. Pat. No. 9,623,393, and 8,535,381.
Microchannel reactors, which term is intended by definition to include monolith reactors, are well suited for a vapor phase dehydrogenation process. They offer ability to effect the dehydrogenation of hydrogen fuel sources while obtaining excellent heat transfer and mass transfer. One can pump the liquid fuel to a vaporizer which then enters a reactor containing the appropriate catalyst. Thus, pressure drop does not become an insurmountable problem as it is in gas phase production of hydrogen. Microchannel reactors and monolith reactors are known in the art. The microchannel reactors are characterized as having at least one reaction channel having a dimension (wall-to-wall, not counting catalyst) of 2.0 mm (preferably 1.0 mm) or less, and in some embodiments 50 to 500 μm. The height and/or width of a reaction microchannel is preferably 2 mm or less, and more preferably 1 mm or less. The channel cross section may be square, rectangular, circular, elliptical, etc. The length of a reaction channel is parallel to flow through the channel. These walls are preferably made of a nonreactive material which is durable and has good thermal conductivity. Most microchannel reactors incorporate adjacent heat transfer microchannels, and in practice, such reactor scheme generally is necessary to provide the heat required for the endothermic dehydrogenation. Illustrative microchannel reactors are shown in U.S. 2004/0199039 and U.S. Pat. No. 6,488,838 and are incorporated by reference herein. Monolith supports, which may be catalytically modified and used for catalytic dehydrogenation, are honeycomb structures of long narrow capillary channels, circular, square or rectangular, whereby the vaporized fuel and generated dehydrogenated product and hydrogen gas can co-currently pass through the channels. Typical dimensions for a honeycomb monolith catalytic reactor cell wall spacing range from 1 to 10 mm between the plates. Alternatively, the monolith support may have from 100 to 800, preferably 200 to 600 cells per square inch (cpi). Channels or cells may be square, hexagonal, circular, elliptical, etc. in shape.
In a representative dehydrogenation process, a liquid fuel, such as tetrahydrothiophene, is vaporized by means of a pump to a reaction pressure, e.g., 1000 psia and delivered via a manifold to a plurality of reaction chambers (monoliths) within a first microchannel reactor. Overall dehydrogenation pressures may range from 0.2 to 100 atmospheres. Dehydrogenation catalyst particles are packed within the monoliths, although, as an alternative, the catalyst may be embedded, impregnated or coated onto the wall surface of the monoliths. The reaction channel through the monoliths may be a straight channel or with internal features such that it offers a large surface area to volume of the channel.
According to the prior art, heat is supplied to the microchannel reactor by a series of band heaters. Alternatively, there may be a circulating a heat exchange fluid through a series of heat exchange channels adjacent to the monoliths. The heat exchange fluid may advantageously carry waste heat, such as a gaseous byproduct of combustion which may be generated in a hybrid vehicle or hydrogen internal combustion engine or it may be a heat exchange fluid employed for removing heat from fuel cell operation. In some cases, where a liquid heat exchange fluid is employed, as for example heat exchange fluid from a fuel cell, supplemental heat may be added, through the use of a combustion gas or thermoelectric unit. The heat exchange fluid from a PEM (proton exchange membrane) fuel cell typically is recovered at a temperature of about 80° C., which is at the low end of the temperature for dehydrogenation. By the use of combustion gases it is possible to raise the temperature of the heat exchange fluid to provide the necessary heat input to support dehydrogenation of many of the fuel sources. A heat exchange fluid from fuel cells that operate at higher temperatures, e.g., 400° C. may also be employed. Dehydrogenation is typically carried out in microchannel reactor at a temperature of generally from about 200 to 400° C. Dehydrogenation is favored by higher temperatures, elevated temperatures; e.g., 400° C. and above may be required to obtain a desired dehydrogenation reaction rate.
All references cited herein are expressly incorporated by reference in their entirety.